Apparatus and method for wireless communication via at least one of directional and omni-direction antennas

ABSTRACT

Techniques for using at least one of omni-directional and directional antennas for communication are described. A station may be equipped antenna elements selectable for use as an omni-directional antenna or one or more directional antennas. The station may select the omni-directional antenna or a directional antenna for use for communication based on various factors such as, e.g., whether the location or direction of a target station for communication is known, whether control frames or data frames are being exchanged, etc.

I. CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent is a divisional of patent applicationSer. No. 11/758,578 entitled “APPARATUS AND METHOD FOR WIRELESSCOMMUNICATION VIA AT LEAST ONE OF DIRECTIONAL AND OMNI-DIRECTIONANTENNAS” filed Jun. 5, 2007, pending, which claims priority toProvisional Application Ser. No. 60/811,578, which was assigned AttorneyDocket No. 061377P1, entitled “DIRECTIONAL ANTENNA UTILIZATION INWIRELESS MESH NETWORKS,” filed Jun. 6, 2006, assigned to the assigneehereof, and expressly incorporated herein by reference.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to data transmission and reception in a wirelesscommunication network.

II. Background

A wireless communication network may include many stations that maycommunicate with one another via a wireless medium. Each station may bestationary or mobile and may be located anywhere within the wirelessnetwork. A given station A may exchange data with another station B, andeach station may not know the whereabouts of the other station at thetime of the data exchange. Station A may transmit in all directions toimprove the likelihood of successful reception by station B. Similarly,station B may receive from all directions to improve the likelihood ofreceiving the transmission from station A. However, the omni-directionaltransmission from station A may cause interference to other stations inthe vicinity. Similarly, the omni-directional reception by station B mayresult in reception of more interference from other stations. Theinterference caused by station A and the interference received bystation B may adversely impact the performance of all affected stations.

There is therefore a need in the art for techniques to improveperformance of data transmission and reception in a wirelesscommunication network.

SUMMARY

Techniques for using at least one of omni-directional and directionalantennas for communication are described herein. A directional antennais an antenna that can transmit and/or receive data via a beamwidth thatis less than 360°, e.g., from 10° to 120°. An omni-directional antennais an antenna that can transmit and/or receive data via all or most of360°. An omni-directional antenna may be a specially designed antenna ormay be formed or synthesized with multiple directional antennas.

In an aspect, a station may be equipped with antenna elements selectablefor communication as an omni-directional antenna or one or moredirectional antennas, which may be implemented in various manners asdescribed below. From the antenna elements, the station may select theomni-directional antenna or a directional antenna for use forcommunication based on various factors such as, e.g., whether thelocation or direction of a target station for communication is known,whether control frames or data frames are being exchanged, etc. Inanother aspect, the station may select a particular directional antennafrom among multiple directional antennas available for use in variousmanners. For example, the station may estimate received signal strengthor received signal quality of a transmission from the target station foreach of the multiple directional antennas and may select the directionalantenna with the highest received signal strength or quality. Thestation may also select the directional antenna based on the location ordirection of the target station, which may be known a priori ordetermined based on any positioning techniques.

In one specific design that is applicable for IEEE 802.11, the stationuses an omni-directional antenna and a directional antenna forcommunicating a Request to Send and Clear to Send (RTS/CTS) with thetarget station. The station may receive a RTS frame from the targetstation via the omni-directional antenna and may select a directionalantenna, e.g., based on the arrival direction of the RTS frame. Thestation may send a CTS frame to the target station via theomni-directional antenna. The station may then receive one or more dataframes from the target station via the selected directional antenna fora duration indicated by the RTS frame. The station may switch back tothe omni-directional antenna after this duration.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless local area network (WLAN).

FIG. 2 shows a wireless mesh network.

FIG. 3 shows a block diagram of two stations in a wireless network.

FIGS. 4A, 4B and 4C show three designs of omni-directional anddirectional antennas.

FIG. 5A shows an example omni-directional beam pattern.

FIG. 5B shows an example directional beam pattern.

FIGS. 6A and 6B show a process and an apparatus, respectively, forantenna selection.

FIG. 7 shows a process for sector selection.

FIG. 8 shows a process for rate selection.

FIGS. 9A and 9B show a process and an apparatus, respectively, foroperating a station on two links.

FIGS. 10A and 10B show a process and an apparatus, respectively, fortransmitting data frames in an RTS/CTS exchange.

FIGS. 11A and 11B show a process and an apparatus, respectively, forreceiving data frames in an RTS/CTS exchange.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein are merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein.

The techniques described herein may be used for various wirelesscommunication networks such as wireless local area networks (WLANs),wireless metropolitan area networks (WMANs), wireless wide area networks(WWANs), wireless mesh networks, etc. The terms “networks” and “systems”are often used interchangeably. A WLAN may implement any of the radiotechnologies in the IEEE 802.11 family of standards, Hiperlan, etc. AWMAN may implement IEEE 802.16, etc. A WWAN may be a cellular networksuch as a Code Division Multiple Access (CDMA) network, a Time DivisionMultiple Access (TDMA) network, a Frequency Division Multiple Access(FDMA) network, an Orthogonal FDMA (OFDMA) network, a Single-CarrierFDMA (SC-FDMA) network, etc. Certain aspects of the techniques aredescribed below for wireless networks that implement IEEE 802.11.

FIG. 1 shows a WLAN 100 with an access point 110 and multiple stations120. In general, a WLAN may include any number of access points and anynumber of stations. A station is a device that can communicate withanother station via a wireless medium. A station may also be referred toas a terminal, a mobile station, a user equipment, a subscriber station,etc. A station may be a cellular phone, a handheld device, a wirelessdevice, a personal digital assistant (PDA), a laptop computer, awireless modem, a cordless phone, etc. An access point is a station thatprovides access to distribution services via the wireless medium forstations associated with that access point. An access point may also bereferred to as a base station, a base transceiver station (BTS), a NodeB, etc. Stations 120 may communicate with access point 110 and/or withone another via peer-to-peer communication. Access point 110 may coupleto a data network 130 and may communicate with other devices via thedata network. Data network 130 may be the Internet, an intranet, or someother wired or unwired network.

FIG. 2 shows a wireless mesh network 200 that may be deployed over anarea such as, e.g., a campus area, an urban center, a mall, or someother hot zone typically characterized by higher population density.Wireless mesh network 200 may operate in accordance with an IEEE 802.11radio technology or some other radio technology. Wireless mesh network200 includes a number of nodes, which are referred to as mesh points220, 230 and 240. Mesh points 220 and 230 may forward traffic for othermesh points. Mesh points 240 are leaf mesh points that do not forwardtraffic for other mesh points.

In general, each mesh point may be a station or an access point. In theexample shown in FIG. 2, mesh points 220 and 230 may be access points,and mesh points 240 may be leaf stations and/or access points. Accesspoints 220 may be connected directly to a backhaul network 210, whichmay be a wired infrastructure acting as the backbone for wireless meshnetwork 200. Deployment and operating costs may be reduced by havingonly a subset of the access points connected directly to backhaulnetwork 210. Access points 230 may communicate with one another and/orwith access points 220 via inter-access point mesh communication inorder to exchange traffic via backhaul network 210. Access points 230may act as entities that forward traffic to access points 220. Leafstations 240 may communicate with access points 220 and/or 230.

In mesh network 200, a frame of data (or a packet) may flow from asource to a destination via a route that may consist of one or more meshpoints. A routing algorithm may be used to determine a sequence of meshpoints for the frame to pass through to reach the destination. Incertain situations, an access point may be congested and may requestother access points that forward traffic to the congested access pointto slow down in order to decongest the network.

FIG. 3 shows a block diagram of a design of two stations 310 and 350 ina wireless network. For WLAN 100 in FIG. 1, station 310 may be accesspoint 110, and station 350 may be one of stations 120. Station 310 mayalso be one of stations 120, and station 350 may be access point 110.For mesh network 200 in FIG. 2, stations 310 and 350 may each be meshpoint 220, 230 or 240. In general, a “station” in the description hereinmay be either a station (STA) that does not provide access todistribution services or an access point (AP) that provides access todistribution services.

Station 310 may use multiple (T) antenna elements 320 a through 320 tfor data transmission and reception. Station 350 may use multiple (R)antenna elements 352 a through 352 r for data transmission andreception. In general, T and R may each be any integer value. In somedesigns, T and R may each be equal to 2 or 4. The antenna elements ateach station may be used to synthesize omni-directional and directionalantennas, as described below.

At station 310, a transmit (TX) data processor 312 may receive trafficdata from a data source (not shown) and/or other data from acontroller/selector/processor 330. TX data processor 312 may process(e.g., format, encode, interleave, and symbol map) the received data andgenerate data symbols, which are modulation symbols for data. A TXspatial processor 314 may multiplex the data symbols with pilot symbols,perform transmit spatial processing if applicable, and provide T streamsof output symbols to a modulator (MOD), demodulator (DEMOD), and switchunit 318. Unit 318 may perform modulation on each output symbol stream(e.g., for OFDM, etc.) and generate an output chip stream. Unit 318 mayfurther condition (e.g., convert to analog, amplify, filter, frequencyupconvert, and power amplify) each output chip stream to generate aradio frequency (RF) signal. Unit 318 may route T RF signals to Tantenna elements 320 a through 320 t, which may transmit these RFsignals.

At station 350, R antenna elements 352 a through 352 r may receive theRF signals transmitted by station 310, and each antenna 352 may providea received signal to a modulator, demodulator, and switch unit 360. Unit360 may process (e.g., demodulate and condition) each received signal ina manner complementary to the processing performed by unit 318 to obtainreceived symbols. A receive (RX) spatial processor 360 may performspatial matched filtering on the received symbols from all R antennaelements 352 a through 352 r and provide data symbol estimates, whichare estimates of the data symbols transmitted by station 310. An RX dataprocessor 362 may further process (e.g., symbol demap, deinterleave, anddecode) the data symbol estimates and provide decoded data to a datasink (not shown) and/or a controller/selector/processor 370.

A channel processor 374 may process the received symbols from unit 360to derive a channel estimate for station 310, received signal strengthand/or received signal quality for a received transmission, aninterference estimate, etc. Processor 374 may derive spatial filtermatrices used by RX spatial processor 360 for spatial matched filtering.Processor 374 may also derive transmit steering matrices used by TXspatial processor 314 for transmission. Processor 374 may also determineother characteristics of the wireless medium and/or receivedtransmission, as described below.

The processing for transmission from station 350 to station 310 may bethe same as or different from the processing for transmission fromstation 310 to station 350. At station 350, traffic data from a datasource (not shown) and/or other data (e.g., feedback information) fromcontroller/selector/processor 370 may be processed (e.g., encoded,interleaved, and symbol mapped) by a TX data processor 380, multiplexedwith pilot symbols and spatially processed by a TX spatial processor382, and further processed (e.g., modulated and conditioned) by unit 360to generate R RF signals, which may be transmitted via antenna elements352 a through 352 r.

At station 310, the RF signals transmitted by station 350 may bereceived by antenna elements 320 a through 320 t and processed by unit318 to obtain received symbols. The received symbols may be processed(e.g., spatial matched filtered) by an RX spatial processor 340 andfurther processed (e.g., symbol demapped, deinterleaved, and decoded) byan RX data processor 342 to obtain decoded data. A channel processor 334may process the received symbols from unit 318 to derive a channelestimate for station 350, received signal strength or received signalquality for a received transmission, an interference estimate, etc.Processor 334 may derive spatial filter matrices, transmit steeringmatrices, etc., based on the channel estimate. Processor 334 may alsodetermine other characteristics of the wireless medium and/or receivedtransmission.

Controllers/selectors/processors 330 and 370 may control the operationat stations 310 and 350, respectively. For example,controllers/selectors/processors 330 and 370 may select anomni-directional antenna or a directional antenna for use forcommunication. Memories 332 and 372 may store data and program codes forstations 310 and 350, respectively.

In an aspect, a station may be equipped with an omni-directional antennaand one or more directional antennas that may be used for datatransmission and/or reception. In general, an antenna may comprise asingle antenna element or a collection of antenna elements. Theomni-directional and directional antennas may be implemented withvarious designs. These antennas may be formed with different antennaelements or may share common antenna elements. The omni-directional anddirectional antennas may also be selected for use in various manners.

FIG. 4A shows a block diagram of a design 410 of omni-directional anddirectional antennas for station 310 in FIG. 3. In this design, station310 includes T antenna elements 320 a through 320 t coupled to a unit318 a, which is one design of unit 318 in FIG. 3.

In the design shown in FIG. 4A, each antenna element 320 is associatedwith a multiplier 412, a switch 414, a modulator 416, and a demodulator418. For data transmission via antenna element 320 a, modulator 416 aprovides a modulated signal to switch 414 a, which routes the signal tomultiplier 412 a. Multiplier 412 a multiplies the modulated signal witha weight w₁ and provides an RF signal to antenna 320 a. For datareception via antenna element 320 a, multiplier 320 a multiplies areceived signal from antenna element 320 a with the weight w₁ andprovides a scaled signal. Switch 414 a routes the scaled signal frommultiplier 412 a to demodulator 418 a. The signals for each of antennaelements 320 b through 320 t may be routed and scaled in similar manneras the signals for antenna element 320 a.

The weights w₁ through w_(T) may be selected to synthesize anomni-directional beam or a directional beam with antenna elements 320 athrough 320 t. The weights may be dependent on the design and placementof antenna elements 320 a through 320 t, the desired beam, and possiblyother factors. The weights may be determined based on computersimulation, empirical measurements, etc. The weights w₁ through w_(T)may be applied to RF signals as shown in FIG. 4A or on analog signalswithin modulators 416 and demodulators 418. The weights w₁ through w_(T)may also be applied to digital signals in the transmit path by TXspatial processor 314 in FIG. 3 and/or to digital signals in the receivepath by RX spatial processor 340.

In general, antenna elements 320 a through 320 t may be used tosynthesize any number of directional antennas. In one design, antennaelements 320 a through 320 t are used to synthesize three directionalantennas that point outwardly with approximately 120° of separation. Thebeam for each directional antenna may have a beamwidth of over 120° andmay overlap adjacent beams at the edges. Fewer or more directionalantennas may also be synthesized. In general, antenna elements 320 athrough 320 t may be used to synthesize any number of directionalantennas that may point at specific directions (e.g., 120° apart) or maybe spaced apart in small angle increments.

FIG. 4B shows a block diagram of a design 430 of omni-directional anddirectional antennas for station 310 in FIG. 3. In this design, station310 includes four sets of T antenna elements coupled to a unit 318 b,which is another design of unit 318 in FIG. 3. The first set includes Tantenna elements 320 a 0 through 320 t 0 for an omni-directionalantenna. The second set includes T antenna elements 320 a 1 through 320t 1 for a directional antenna for sector 1. The third set includes Tantenna elements 320 a 2 through 320 t 2 for a directional antenna forsector 2. The fourth set includes T antenna elements 320 a 3 through 320t 3 for a directional antenna for sector 3. The three directionalantennas for the three sectors may point outwardly with approximately120° of separation, and each directional antenna may have a beamwidth ofover 120°. Each set of antenna elements may be designed to achieve thedesired beam for the corresponding omni-directional or directionalantenna. Improved performance may be achieved by using a different setof antenna elements for each antenna beam.

One of the four sets of antenna elements may be selected for use forcommunication. The selected set of T antenna elements may correspond toantenna elements 320 a through 320 t in FIG. 3.

Unit 318 b includes T switches 434 a through 434 t, T modulators 436 athrough 436 t, and T demodulators 438 a through 438 t. Switch 434 acouples to four antenna elements 320 a 0, 320 a 1, 320 a 2 and 320 a 3in the four sets and further to modulator 436 a and demodulator 438 a.For data transmission, switch 434 a couples the modulated signal frommodulator 436 a to an antenna element in the selected set. For datareception, switch 434 a couples the received signal from the antennaelement in the selected set to demodulator 438 a. The switches,modulators, and demodulators for the other antenna elements may becoupled and operated in similar manner as switch 434 a, modulator 436 a,and demodulator 438 a.

FIG. 4C shows a block diagram of a design 450 of omni-directional anddirectional antennas for station 310 in FIG. 3. In this design, station310 includes three sets of T antenna elements coupled to a unit 318 c,which is yet another design of unit 318 in FIG. 3. The first setincludes T antenna elements 320 a 1 through 320 t 1, the second setincludes T antenna elements 320 a 2 through 320 t 2, and the third setincludes T antenna elements 320 a 3 through 320 t 3, which are asdescribed above for FIG. 4B. One of the three sets of antenna elementsmay be selected for a directional antenna, or all three sets may beselected for the omni-directional antenna. A virtual antenna may beformed by combining three antenna elements in the three sets, e.g.,antenna elements 320 a 1, 320 a 2 and 320 a 3.

Unit 318 c includes T sets of circuitry, with each circuitry setincluding switches 452, 454 and 456, a combiner 462, a switch 464, amodulator 466, and a demodulator 468. Switch 452 a couples antennaelement 320 a 1 to combiner 462 a if the omni-direction antenna isselected and to switch 464 a if the directional antenna for sector 1 isselected. Switch 452 b couples antenna element 320 a 2 to combiner 462 aif the omni-direction antenna is selected and to switch 464 a if thedirectional antenna for sector 2 is selected. Switch 452 c couplesantenna element 320 a 3 to combiner 462 a if the omni-direction antennais selected and to switch 464 a if the directional antenna for sector 3is selected. For data transmission, combiner 462 a receives the signalfrom switch 464 a and provides the signal to switches 452 a, 452 b and452 c. For data reception, combiner 462 a combines the received signalsfrom switches 452 a, 452 b and 452 c and provides the combined signal toswitch 464 a. For data transmission, switch 464 a couples the modulatedsignal from modulator 466 a to switch 452 a, 452 b or 452 c or combiner462 a. For data reception, switch 434 a couples the signal from switch452 a, 452 b or 452 c or combiner 462 a to demodulator 438 a. Theswitches, combiners, modulators, and demodulators for the other antennaelements may be coupled and operated in similar manner as those for thefirst antenna element.

In another design, station 310 includes (1) a first set of at least oneantenna for communication with other stations in the wireless networkand (2) a second set of at least one antenna for communication withanother network, e.g., a backhaul network. The first antenna set may bedesigned for a first frequency band, e.g., 2.4 GHz or 5 GHz used forIEEE 802.11, or some other frequency band. The second antenna set may bedesigned for a second frequency band, e.g., 3.5 GHz or some otherfrequency band. An antenna set may include both omni-directional anddirectional antennas and may be implemented as shown in FIG. 4A, 4B, or4C. Alternatively, an antenna set may include just an omni-directionalantenna. In one design, the first set includes just an omni-directionalantenna while the second set includes both omni-directional anddirectional antennas. Separate transmit and receive circuitry may beused for the two antenna sets. In this case, station 310 may be able tosimultaneously communicate with two stations via the two antenna sets,e.g., with a station in a mesh network via the first antenna set andwith a mesh access point via the second antenna set.

FIG. 5A shows an example omni-directional beam pattern, which may beobtained with the antenna design shown in FIG. 4A, 4B or 4C. Thisomni-directional beam pattern has similar antenna gains for all spatialdirections.

FIG. 5B shows an example directional beam pattern, which may be obtainedwith the antenna design shown in FIG. 4A, 4B or 4C. This directionalbeam pattern has high antenna gains across a beamwidth and small antennagains outside of the beamwidth. The beamwidth may be selected based onthe number of sectors being supported and the desired amount of overlapbetween directional beams.

FIGS. 4A to 4C show three example designs for omni-directional anddirectional antennas, which may be used for stations 310 and 350. Theomni-directional and directional antennas may also be implemented withother designs. These antennas may also be implemented with any number ofantenna elements. An antenna element may be a dipole antenna, a patchantenna, a microstrip antenna, a stripline antenna, a printed dipoleantenna, an inverted F antenna, etc.

The following aspects may be applicable for communication betweenstations 310 and 350:

-   -   Antenna selection—refers to selection of the omni-directional        antenna or a directional antenna for use for communication,    -   Sector section—refers to selection of a particular directional        antenna from among all directional antennas available for use at        a station, and    -   Rate selection—refers to selection of one or more data rates for        transmission.        For clarity, much of the following description is from the        perspective of station 310. Station 350 is a target station,        which is a station with which packets are exchanged, e.g., sent        and/or received.

Antenna selection may be performed based on various criteria such aswhether or not the location or direction of target station 350 is known,the type of information being sent or received, received signalstrength/quality for target station 350, interference from otherstations, etc. In one design, the omni-directional antenna is selectedfor use if the location or direction of target station 350 is not knownor if multiple stations are being targeted. Station 310 may receive aframe from any station in the wireless network at any given moment.Station 310 may use the omni-directional antenna to receive frames fromstations at unknown locations. Station 310 may also transmit frames tostations at unknown locations using the omni-directional antenna.Station 310 may also use the omni-directional antenna to send a givenframe (e.g., a control frame) to multiple stations at known or unknownlocations.

In one design, a directional antenna is selected for use if the locationor direction of target station 350 is known. The location or directionof target station 350 may be ascertained based on a transmission sent bytarget station 350, a location estimate for target station 350, etc.

Station 310 may select the omni-directional or direction antenna for usefor communication with target station 350 based on context. Station 310may also select the omni-directional or direction antenna autonomouslywithout input from target station 350. The use of a directional antenna,when possible, may increase spatial reuse in the wireless network, whichmay improve overall performance.

Sector selection may be performed in various manners. In one design,sector selection is performed based on received signal strength orreceived power. Station 310 may receive a transmission from targetstation 350 via each of the directional antennas available at station310. Station 310 may determine the received signal strength for eachdirectional antenna, e.g., by summing the received power of T receivedsignals from T antenna elements for the directional antenna. Station 310may sum the received power for each directional antenna in differentmanners for different antenna designs. For example, station 310 maysynthesize different directional antennas with different sets of weightsapplied by RX spatial processor 340. In this case, station 310 maymultiply the received symbols from unit 318 with a set of weights foreach directional antenna to obtain output symbols for that directionalantenna and may then determine the received signal strength for thedirectional antenna based on the output symbols. In any case, station310 may select the directional antenna with the strongest receivedsignal strength for use.

In another design, sector selection is performed based on receivedsignal quality, which may be given by a signal-to-noise ratio (SNR), asignal-to-noise-and-interference ratio (SINR), a carrier-to-interferenceratio (C/I), etc. Received signal quality takes into consideration thereceived power as well as noise and interference. Hence, received signalquality may be more suitable to select a data rate for datatransmission. Station 310 may receive a transmission from target station350 via each of the directional antennas. Station 310 may determine thereceived signal quality of the transmission for each directional antennaand may select the directional antenna with the highest received signalquality.

In yet another design, sector selection is performed based on priorinformation for target station 350. The location or direction of targetstation 350 may be ascertained, e.g., based on any of the designsdescribed above. A directional antenna may be selected for station 350and stored in memory. Thereafter, if the same target station 350 isencountered, the directional antenna selected previously for thisstation may be retrieved from memory and used for communication with thestation. The retrieved directional antenna may be confirmed, e.g., basedon received signal strength or received signal quality measurement madeduring the current communication, to ensure that the retrieveddirectional antenna is still the best one.

In yet another design, sector selection is performed based on a look-uptable containing information on other stations in the wireless network.The information may comprise the location or direction of each station,the directional antenna applicable for each station, etc. Theinformation may be updated whenever transmissions are received from theother stations.

Rate selection may be performed based on various factors such as thereceived signal quality, the antenna selected for use, the type oftransmission being sent, interference estimate, etc. Different antennasmay be associated with different antenna gains, which may becharacterized and known a priori. One or more data rates may be selectedby taking into account different antenna gains for different antennasused by stations 310 and 350.

Station 310 may use its antenna elements to send or receive asingle-input single-output (SISO) transmission, a single-inputmultiple-output (SIMO) transmission, a multiple-input single-output(MISO) transmission, or a multiple-input multiple-output (MIMO)transmission. For SISO or SIMO, station 310 may send a single datastream via a single virtual antenna corresponding to a selectedomni-directional or directional antenna. For MISO, station 310 may senda single data stream via multiple antenna elements for the selectedantenna. For MIMO, station 310 may send multiple data streamssimultaneously via multiple antenna elements. Each data stream may besent from one antenna element in omni-direction. Each data stream mayalso be sent from all antenna elements with transmit steering, and henceon a directional/virtual antenna selected for that data stream.Different data streams may be sent with different transmit steeringvectors and thus on different directional/virtual antennas.

Station 310 may estimate interference observed via the omni-directionalantenna and each directional antenna. Station 310 may estimate theinterference on a given antenna by measuring the received power for thatantenna when no packets are sent or received by station 350, so that thereceived power may be attributed to transmissions from other stations.Since the other stations may transmit at any time, the interference mayfluctuate over time and may be quantified by statistical parameters. Inone design, the interference for a given antenna may be given by acumulative density function (CDF) that indicates, for a giveninterference level x, the percentage of time the measured interferenceis below x. For example, the CDFs may indicate that the interferencelevel is −85 dBm for 5% of the time for a directional antenna and −75dBm for 5% of the time for the omni-directional antenna.

For data reception, station 310 may estimate the received signal qualityof a transmission from target station 350. Station 310 may select a datarate based on the received signal quality, e.g., using a look-up tableof data rate versus received signal quality. Station 310 may also applya backoff based on an interference estimate. For example, station 310may reduce the received signal quality by an amount determined by theinterference estimate and may select a data rate based on the reducedreceived signal quality. For a MIMO transmission, station 310 mayperform (1) rank selection to determine the number of data streams tosend and (2) stream selection to determine which antenna element orwhich virtual antenna to use for each data stream. Station 310 may alsoperform rate selection to select a suitable data rate for each datastream or one common data rate for all data streams, based on thereceived signal quality and possibly interference estimate.

Station 310 may estimate the received signal quality of a transmissionfrom station 350 based on the omni-directional antenna and may select adirectional antenna for use. In this case, station 310 may adjust thereceived signal quality or the data rate to take into account thedifference in element gains, antenna gains, and/or interferencerejection for the omni-directional and directional antennas. Station 310may also use a data rate determined from the omni-directional antenna asa lower bound for a data rate for the directional antenna.

Station 310 may select one or more data rates for one or more datastreams based on the received signal quality, the difference in antennagains, the interference estimate, etc. Station 310 may send the selecteddata rate(s) to station 350, which may send data at the selected datarate(s).

For data transmission, station 310 may send a transmission to targetstation 350, e.g., using the omni-directional antenna. Station 350 mayestimate the received signal quality, select one or more data ratesbased on the received signal quality, and send the selected data rate(s)to station 310. If station 310 sends the initial transmission with theomni-directional antenna and selects a directional antenna forsubsequent data transmission to station 350, then station 310 may adjustthe data rate(s) received from station 350 to take into account thedifference in element gains, antenna gains, and/or interferencerejection for the omni-directional and directional antennas.

Station 310 may use the interference estimate to backoff the datarate(s). Station 310 may also use the interference estimate to select anantenna. For example, an antenna with less interference may be selectedfor use, or an antenna with excessive interference may be disqualifiedfrom use.

FIG. 6A shows a design of a process 600 for antenna selection. Process600 may be performed by a station, e.g., an access point or a station inIEEE 802.11 WLAN or mesh network. An omni-directional antenna or adirectional antenna may be selected for use for communication (block612). The antenna selection in block 612 may be performed in variousmanners and based on various factors. In one design, theomni-directional antenna may be selected if the location or direction ofa target station for communication is unknown, and the directionalantenna may be selected if the location or direction of the targetstation is known. In another design, the omni-directional antenna may beselected for control frames, and the directional antenna may be selectedfor data frames and if the location or direction of the target stationis known. The directional antenna may be selected from among multiple(e.g., three) directional antennas available for use or may besynthesized based on a transmission received from the target station.The selected antenna may be used for communication, e.g., to send and/orreceive data (block 614).

The omni-directional and directional antennas may be obtained in variousmanners. In one design, a set of antenna elements may be usable forcommunication. The omni-directional and directional antennas may besynthesized with this set of antenna elements, e.g., as shown in FIG.4A. In another design, the omni-directional antenna may be implementedwith at least one antenna element, and at least one directional antennamay be implemented with at least one set of antenna elements, e.g., asshown in FIG. 4B. In yet another design, multiple directional antennasmay be implemented with multiple sets of antenna elements, and theomni-directional antenna may be formed with the multiple sets of antennaelements, e.g., as shown in FIG. 4C. The omni-directional anddirectional antennas may be implemented or synthesized in other manners.

FIG. 6B shows a design of an apparatus 650 for antenna selection.Apparatus 650 includes means for selecting an omni-directional antennaor a directional antenna for use for communication (module 652), andmeans for using the selected antenna for communication, e.g., to sendand/or receive data (module 654). Modules 652 and 654 may comprise oneor more integrated circuits (ICs), processors, electronics devices,hardware devices, electronics components, logical circuits, memories,etc., or any combination thereof.

FIG. 7 shows a design of a process 700 for sector selection. Atransmission (e.g., for a control frame) may be received from a station(block 712). The transmission may be received via an omni-directionalantenna, which may be a true omni-directional antenna or synthesizedwith multiple directional antennas, e.g., by receiving the transmissionvia all of these directional antennas. A directional antenna may beselected from a set of antennas based on the received transmission(block 714). The set of antennas may comprise only directional antennasor both omni-directional and directional antennas. Multiple directionalantennas may be implemented with different sets of antenna elements(e.g., as shown in FIGS. 4B and 4C) or may be synthesized based on asingle set of antenna elements (e.g., as shown in FIG. 4A). In onedesign, the direction of arrival of the transmission may be determined.The directional antenna that is closest to the arrival direction of thetransmission may be selected from among multiple directional antennasavailable for use. In another design, at least one antenna element maybe tuned to the arrival direction of the transmission. In yet anotherdesign, the received signal strength of the transmission may bedetermined for each of the multiple directional antennas, and thedirectional antenna with the highest received signal strength may beselected. In yet another design, the received signal quality of thetransmission may be determined for each of the multiple directionalantennas, and the directional antenna with the highest received signalquality may be selected. The directional antenna may also be selectedbased on an interference estimate.

The selected directional antenna may be used for communication with thestation (block 716). For data reception, at least one data frame may bereceived from the station via the selected directional antenna. For datatransmission, at least one data frame may be sent to the station via theselected directional antenna.

FIG. 8 shows a design of a process 800 for rate selection. Atransmission from a station may be received via an omni-directionalantenna (block 812). A directional antenna may be selected based on thereceived transmission (block 814). A data rate may be selected based onthe received transmission and the selected directional antenna (block816). Data may be exchanged with the station via the selecteddirectional antenna and in accordance with the selected data rate (block818).

For block 816, the received signal quality of the transmission may beestimated. Interference for the selected directional antenna may also beestimated. The difference between the antenna gain of theomni-directional antenna and the antenna gain of the selecteddirectional antenna may be determined. The data rate may be selectedbased on the received signal quality, the interference estimate, thedifference in antenna gains, or any combination thereof. The data ratemay also be selected based on other factors. One or more rates may beselected for a MIMO transmission, depending on how data streams areprocessed and sent.

FIG. 9A shows a design of a process 900 for operating a station on twolinks. The station may communicate with a first station on a first linkvia an omni-directional antenna (block 912). The station may communicatewith a second station on a second link via a directional antenna (block914). The first link may be for a wireless medium shared by stations ina wireless network, e.g., an IEEE 802.11 WLAN or mesh network. Thesecond link may be for a backhaul to a wired access point. The first andsecond links may be for the same or different frequency bands. Thestation may simultaneously communicate with the first station on a firstfrequency band and with the second station on a second frequency band.The first and second frequency bands may or may not overlap. If thesefrequency bands overlap, then they may overlap partially, or onefrequency band may completely overlap the other frequency band.

The first and second links may be for the same wireless network, and thefirst and second stations may be the same station. In one design,control frames may be exchanged on the first link via theomni-directional antenna, and data frames may be exchanged on the secondlink via the directional antenna. The omni-directional may be usedminimally, e.g., to capture a small amount of data so as to determinewhich directional antenna should be used.

FIG. 9B shows a design of an apparatus 950 for operating on two links.Apparatus 950 includes means for communicating with a first station on afirst link via an omni-directional antenna (block 952) and means forcommunicating with a second station on a second link via a directionalantenna (block 954). Modules 952 and 954 may comprise one or more ICs,processors, electronics devices, hardware devices, electronicscomponents, logical circuits, memories, etc., or any combinationthereof.

The omni-directional and directional antennas may be used forcommunication in various manners. One specific use of these antennas forcommunication is described below.

In IEEE 802.11, stations contend for the wireless medium through aCarrier Sense Multiple Access with Collision Avoidance (CSMA/CA)protocol, which prevents neighbor stations from transmittingsimultaneously. In addition, a station may reserve a certain amount oftime for transmission on the wireless medium by using an RTS/CTSexchange. For this exchange, a given station A may send an RTS framecontaining a requested duration to another station B, which may be anaccess point for this exchange. The requested duration may cover theamount of time needed to transmit pending data and associated signaling.Station B may grant the request and send a CTS frame to station A.Station A may then transmit on the wireless medium for the grantedduration.

The RTS/CTS exchange is intended to prevent interference from hiddennodes, which are stations that are out of communication range of oneanother but can still cause interference to each other. For example, twostations on opposite sides of an access point may be hidden from oneanother but their transmissions may interfere with each other at theaccess point. In order for the RTS/CTS exchange to be effective, allneighbor stations in the vicinity of stations A and B should be abledecode the RTS and/or CTS frames and set their network allocation vector(NAV) timers according to the duration included in the RTS and CTSframes. Since the RTS and CTS frames can arrive from any arbitrarydirection, each station may use omni-directional antenna to receivethese frames. In may be desirable for a station to receive all controlframes, such as RTS and CTS frames, via omni-directional antenna at alltimes in order to ensure that these control frames can be received.Nevertheless, there may be neighbor stations that cannot decode the RTSand/or CTS frames, e.g., due to their geographical locations and otherfactors. Consequently, these neighbor stations may not remain silentduring the granted duration, and the transmissions from these neighborstations may interfere with the transmission from station A or B andreduce the effective rate of the transmission.

Directional antennas may be used to reduce the adverse impact ofinterference by suppressing interference that arrives from directionsthat are away from the direction of the transmit and receive stations.This interference suppression may improve SNR and allow for use ofhigher data rate. Therefore, combining the use of RTS/CTS along withdirectional antennas may enhance throughput.

FIG. 10A shows a design of a process 1000 performed by transmit stationA for an RTS/CTS exchange. Initially, station A selects theomni-directional antenna for transmission (block 1012). Station Atransmits an RTS frame containing a requested duration to receivestation B via the omni-directional antenna (block 1014). Thereafter,station A receives a CTS frame from station B (block 1016) anddetermines the arrival direction of the CTS frame, e.g., using any ofthe designs described above (block 1018). Station A selects adirectional antenna that is closest to the arrival direction of the CTSframe, which is the direction of receive station B (block 1020). StationA then transmits one or more data frames to station B via the selecteddirectional antenna starting within a short interframe space (SIFS) timeand for the granted duration (block 1022). Station B may receive thedata frames from station A using an omni-directional or a directionalantenna. Transmit station A may switch back to the omni-directionalantenna after the granted duration.

Transmit station A may cause less interference to other stations bytransmitting data frames to receive station B using a directionalantenna. Furthermore, the directional antenna may have higher gain thanthe omni-directional antenna, which may allow for use of higher datarate for the transmission from station A to station B. Station A mayrevert to omni-directional transmission once the data transmission tostation B is over.

FIG. 10B shows a design of an apparatus 1050 for an RTS/CTS exchange.Apparatus 1050 includes means for selecting an omni-directional antennafor transmission (module 1052), means for transmitting an RTS framecontaining a requested duration to receive station B via theomni-directional antenna (module 1054), means for receiving a CTS framefrom station B (module 1056), means for determining the arrivaldirection of the CTS frame (module 1058), means for selecting adirectional antenna that is closest to the arrival direction of the CTSframe (module 1060), and means for transmitting one or more data framesto receive station B via the selected directional antenna startingwithin a SIFS time and for the granted duration (module 1062). Modules1052 through 1062 may comprise one or more ICs, processors, electronicsdevices, hardware devices, electronics components, logical circuits,memories, etc., or any combination thereof.

In the design shown in FIGS. 10A and 10B, transmit station A usesdirectional data transmission for the duration of the RTS/CTS exchangeif the direction of receive station B is known. Station A usesomni-directional transmission at other times when the direction of therecipient stations may not be known. Station A thus uses directionaltransmission in a manner that is backward compatible with IEEE 802.11and yet may enhance throughput.

FIG. 11A shows a design of a process 1100 performed by receive station Bfor an RTS/CTS exchange. Initially, station B selects theomni-directional antenna for data reception (block 1112). Station Breceives an RTS frame from transmit station A and determines theintended destination/recipient of this RTS frame (block 1114). Ifstation B is the destination of the RTS frame (‘Yes’ for block 1116),then station B transmits a CTS frame via the omni-directional antenna(block 1118). Station B determines the arrival direction of the RTSframe, e.g., using any of the designs described above (block 1120).Station B selects a directional antenna that is closest to the arrivaldirection of the RTS frame, which is the direction of transmit station A(block 1122).

Transmit station A receives the CTS frame and may begin transmittingdata frames using an omni-directional antenna or a directional antenna.If receive station B detects data within SIFS time (‘Yes’ for block1124), then station B receives one or more data frames from station Avia the selected directional antenna for the granted duration (block1126). Station B may switch back to the omni-directional antenna afterthe granted duration, or if data was not detected from station A withinSIFS time (‘No’ for block 1124), or if station B is not the intendedrecipient of the RTS frame (‘No’ for block 1116).

Since station B receives data frames from station A using a directionalantenna, interference from other stations may be suppressed. Hence, ahigher data rate may be used for the transmission from station A tostation B than what may be possible without directional reception.Station B may revert to omni-directional reception once the datatransmission from station A is over.

FIG. 11B shows a design of an apparatus 1150 for an RTS/CTS exchange.Apparatus 1150 includes means for selecting an omni-directional antennafor data reception (block 1152), means for receiving an RTS frame fromtransmit station A and determining the intended destination/recipient ofthis RTS frame (block 1154), means for transmitting a CTS frame via theomni-directional antenna (block 1156), means for determining the arrivaldirection of the RTS frame (block 1158), means for selecting adirectional antenna that is closest to the arrival direction of the RTSframe (block 1160), and means for receiving one or more data frames fromstation A via the selected directional antenna for the granted duration(block 1162). Modules 1152 through 1162 may comprise one or more ICs,processors, electronics devices, hardware devices, electronicscomponents, logical circuits, memories, etc., or any combinationthereof.

In the design shown in FIGS. 11A and 11B, receive station B usesdirectional reception for the duration of the RTS/CTS exchange if thedirection of transmit station A is known. Station B usesomni-directional reception at other times when the direction of transmitstations may not be known. Station B thus uses directional reception ina manner that is backward compatible with IEEE 802.11 and yet mayenhance throughput.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anintegrated circuit (IC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. An IC may be an application specificintegrated circuit (ASIC) and may include one or more processors,memories, etc., or any combination thereof. A general-purpose processormay be a microprocessor, but in the alternative, the processor may beany conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration. An apparatusimplementing the techniques described herein may be an IC, a device thatincludes an IC or a set of ICs, any one or combination of the hardwareunits described above, etc.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anIC. The IC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the scope of thedisclosure. Thus, the disclosure is not intended to be limited to theexamples and designs described herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

1. An apparatus for wireless communication, comprising: at least oneintegrated circuit configured to send a Request to Send (RTS) frame to astation via an omni-directional antenna, to receive a Clear to Send(CTS) frame from the station, to select a directional antenna based onthe CTS frame, and to send at least one data frame to the station viathe selected directional antenna.
 2. The apparatus of claim 1, whereinthe at least one integrated circuit is configured to determine receivedsignal strength of the CTS frame for each of multiple directionalantennas, and to select the directional antenna with highest receivedsignal strength.
 3. A method for wireless communication, comprising:sending a Request to Send (RTS) frame to a station via anomni-directional antenna; receiving a Clear to Send (CTS) frame from thestation; selecting a directional antenna based on the CTS frame; andsending at least one data frame to the station via the selecteddirectional antenna.
 4. An apparatus for wireless communication,comprising: means for sending a Request to Send (RTS) frame to a stationvia an omni-directional antenna; means for receiving a Clear to Send(CTS) frame from the station; means for selecting a directional antennabased on the CTS frame; and means for sending at least one data frame tothe station via the selected directional antenna.
 5. An apparatus forwireless communication, comprising: at least one integrated circuitconfigured to receive a Request to Send (RTS) frame from a station viaan omni-directional antenna, to select a directional antenna based onthe RTS frame, and to receive at least one data frame from the stationvia the selected directional antenna.
 6. The apparatus of claim 5,wherein the at least one integrated circuit is configured to send aClear to Send (CTS) frame via the omni-directional antenna.
 7. Theapparatus of claim 5, wherein the at least one integrated circuit isconfigured to determine received signal strength of the RTS frame foreach of multiple directional antennas, and to select the directionalantenna with highest received signal strength among the multipledirectional antennas.
 8. The apparatus of claim 5, wherein the at leastone integrated circuit is configured to determine location or directionof the station sending the RTS frame, and to select the directionalantenna based on the location or direction of the station.
 9. Theapparatus of claim 5, wherein the at least one integrated circuit isconfigured to determine received signal quality based on the RTS frame,to select a data rate based on the received signal quality and theselected directional antenna, and to exchange data with the stationaccording to the selected data rate.
 10. The apparatus of claim 5,wherein the at least one integrated circuit is configured to use thedirectional antenna for a duration indicated by the RTS frame, and toswitch to the omni-directional antenna after the duration.
 11. A methodfor wireless communication, comprising: receiving a Request to Send(RTS) frame from a station via an omni-directional antenna; selecting adirectional antenna based on the RTS frame; and receiving at least onedata frame from the station via the selected directional antenna. 12.The method of claim 11, further comprising: sending a Clear to Send(CTS) frame via the omni-directional antenna.
 13. The method of claim11, wherein the selecting the directional antenna comprises determiningreceived signal strength of the RTS frame for each of multipledirectional antennas, and selecting the directional antenna with highestreceived signal strength among the multiple directional antennas.
 14. Anapparatus for wireless communication, comprising: means for receiving aRequest to Send (RTS) frame from a station via an omni-directionalantenna; means for selecting a directional antenna based on the RTSframe; and means for receiving at least one data frame from the stationvia the selected directional antenna.
 15. The apparatus of claim 14,further comprising: means for sending a Clear to Send (CTS) frame viathe omni-directional antenna.
 16. The apparatus of claim 14, wherein themeans for selecting the directional antenna comprises means fordetermining received signal strength of the RTS frame for each ofmultiple directional antennas, and means for selecting the directionalantenna with highest received signal strength among the multipledirectional antennas.